Heretofore, research and development has been conducted on planar light emitting devices that utilize an organic electroluminescent element (hereinafter, simply referred to as “organic EL element”) in various places (for example, Patent Literature 1). Note that Patent Literature 1 describes an organic EL element formed on a substrate and has a structure in which an anode, a hole transport layer, a light emitting layer, an electron transport layer and a cathode are stacked. With such types of organic EL elements, in the case where the substrate is constituted by a transparent substrate and the anode is constituted by a transparent conductive film such as an ITO film or the like, light emitted from the light emitting layer by applying a voltage between the anode and the cathode is extracted through the anode and the transparent substrate.
Characteristics of organic EL elements include; being self-light emission type light emitting elements, exhibiting a relatively high efficient light emitting properties, enabling light emission in various types of colors, and the like. Therefore, organic EL elements are expected to be applied as display devices (for example, light emitting bodies such as a flat panel display, and the like) and light sources (for example, backlights of liquid crystal display apparatuses, light sources for illumination, and the like), and they have already been put to practical use in some fields. However, in recent years, development of organic EL elements that have a larger area, high efficiency, long service life, and high luminance has been desired in the case of applying organic EL elements to a planar light emitting device.
Patent Literature 1 described above discloses a planar light emitting device in which plural tiles 205 (see FIG. 25) in which organic EL elements are used are arranged in an array as shown in FIG. 24. Note that the tiles constitute flat panel light emitting units in this planar light emitting device.
As shown in FIG. 25, the tile 205 includes a substrate 235 having a square outer shape, a light emitting region 215 for an organic EL element formed on a first surface side of the substrate 235, and eight contacts 210. Here, the tile 205 is provided with four pairs of contacts; each pair consisting of a contact 210 (hereinafter, also referred to as a “first contact 210A”) connected to the anode of the organic EL element and a contact 210 (hereinafter referred to as a “second contact 210K”) connected to the cathode. In the planar light emitting device, adjacent tiles 205 are electrically connected to each other via a pair of the first contact 210A and the second contact 210K.
Also, Patent Literature 1 discloses a tile as the tile 205 that includes a substrate 235, a light emitting region 215 for an organic EL element formed on a first surface side of the substrate 235, a cover 240 that covers the light emitting region 215 on the first surface side of the substrate 235 and is joined to the substrate 235 via seal portions 230, and eight contacts 210. Note that Patent Literature 1 describes that organic EL elements are hermetically sealed along with a desiccating agent because they are likely to be affected by moisture and oxygen.
In the tiles 205 having the configuration shown in FIG. 26, the contacts 210 are formed in a region on the first surface side of the substrate 235 where they do not overlap the cover 240 and in a region on the cover 240 where they do not overlap the substrate 235. In addition, Patent Literature 1 describes that the configuration is not limited to the example in FIG. 26 and that the contacts 210 in the tiles 205 may be configured by exposed regions of the anode and the cathode of an organic EL element. In addition, Patent Literature 1 describes that the shape of the substrate 235 is not limited to the square, and for example, it may be a rectangle, triangle, or hexagon.
Also, Patent Literature 1 discloses a planar light emitting device that includes a back face plate 285 that supports plural tiles 205 described above, as shown in FIG. 27. Here, contacts 296 that allow electrical connection between adjacent tiles 205 are formed on the back face plate 285. Note that in the planar light emitting device having the configuration shown in FIG. 27, the tiles 205 are physically held by holding members 290 on the back face plate 285.
Incidentally, with a planar light emitting device that uses one organic EL element, the sheet resistance of an anode constituted by a transparent conductive film is larger than the sheet resistance of a cathode constituted by a metal film, and therefore in the case where the size of a light emitting area is increased, variation on the plane in the current density of a current that flows through the organic EL element is increased due to a drop in the voltage of the anode, as a result of which variation in luminance increases.
In view of this, it is conceivable that a planar light emitting device is configured by arranging plural tiles 205 side by side in order to increase the size of the light emitting area, as disclosed in Patent Literature 1.